This invention relates generally to insole inserts for footwear which provide protection against penetration of sharp objects through the insole insert, and more particularly relates to insole inserts, whether incorporated into the construction of the footwear itself or fabricated as a separate insert to be positioned inside the completed shoe, which comprise multiple layers of a stainless steel material which is puncture proof under typical conditions expected to be encountered by the user.
Many commercial and construction situations present the danger of sharp object penetration through the soles of footwear worn by workers. A most common example is the presence of nails around construction sites. This dangerous but relatively unavoidable situation results in large numbers of injuries to workers with accompanying lost man-hours, pain suffering, morbidity, infection and medical costs for treatment. Much development has been directed at creating protective footwear which lessens the danger of injury from stepping, jumping or falling onto sharp objects, but much of this development has failed due to the need to balance a high degree of protection with comfort and wearability, since the sole must remain flexible. For example, a relatively thick metal plate is puncture proof under typical conditions but the inflexibility prevents its use as a solution. True puncture prevention rather than mere puncture resistance is difficult to attain. Most of the attempts to create protective footwear have resulted in the creation of footwear which is puncture resistant rather than puncture proof--the typical devices failing to prevent puncture by sharp objects at high impact energy. A 230 pound individual jumping from a height of ten feet generates approximately 60 foot pounds (81.3 joules) on the ball of the foot and approximately 80 foot pounds (108.5 joules) on the heel of the foot, the difference in values resulting from the ability of the foot and leg to better absorb and distribute the force in the ball area rather than at the heel. Exceeding this standard is the goal of a puncture proof insert.
Representative patents showing prior art devices of this nature are such as U.S. Pat. No. 2,803,895 to Frieder et al., showing a multi-layer protective sole consisting of synthetic, resin-impregnated, fibrous laminates, and U.S. Pat. No. 5,285,583 to Aleven, showing a protective insole which incorporates a protective plastic layer between an insole board and a fabric liner. More closely related to the invention at hand are the patents issued to Ashton, Funck and Okayasu et al. The Ashton patent, U.S. Pat. No. 4,888,888, shows a sole formed from a number of small hinged metal plate members joined in the nature of chain mail or two metal plates hinged at the ball position to provide flexibility. The two plate hinged construction does little to increase comfort to the wearer, and the multi-plate chain mail construction is not cost effective with regard to manufacture. The patent to Funck, U.S. Pat. No. 4,271,607, teaches incorporating a single metal plate approximately 0.02 inches thick in the sole of the footwear. Such a device would not meet the prevention requirements for designating the insert puncture proof as opposed to puncture resistant. U.S. Pat. No. 5,003,709 to Okayasu et al. teaches the use of multiple thin metal foils to increase the penetration protection without sacrificing flexibility, but the metal foils are only approximately 0.001 inches thick and even when used in multiple layers as taught would not provide complete protection against punctures unless an exorbitant number of layers were combined, a fact acknowledged in that patent at column 1, lines 29-34. The Okayasu et al. patent also teaches a construction where the foil layers are used only in the ball area and the remainder of the sole is constructed from non-flexible thick metal sheets, a construction which increases the puncture protection in the heel area but which sacrifices flexibility and comfort while increasing manufacturing difficulty and cost. In addition, all of the prior known art provides a planar insole suitable only for incorporation into the footwear prior to manufacture or for use with footwear having no raised arch support. Other patents which include metal in the shoe to provide extra protection are U.S. Pat. No. 2,304,936 to Lewis, U.S. Pat. No. 1,685,538 to Glidden et al., U.S. Pat. No. 4,404,757 to Sweeny and U.S. Pat. No. 1,676,170 to Troiel. The Lewis, Sweeny and Troiel involve multi-component pieces which involve complicated manufacturing steps and severely reduce flexibility. Glidden et al. discloses a weak insert with apertures.
It is an object of this invention to provide a puncture proof insert able to prevent penetration through the insert at energies up to 60 foot pounds in the ball of the foot region and 80 foot pounds in the heel region, while retaining suitable flexibility so as not to impair the comfort and wearability of the insert. It is a further object to provide such an insert where the protection is provided by multiple layers of thin metal sheets and where the number of such sheets is less in the ball region where maximum flexibility is required and greater in the heel region where less flexibility is needed and greater penetration protection is required. It is a further object to provide such an insert in which the metal sheets are approximately 0.015 inches in thickness and where two such sheets are present in the ball region and three sheets are present in the heel region. It is a further object to provide such a puncture proof insole insert which can be incorporated into the body of the footwear during manufacture or which can be constructed as a separate device insertable into the footwear after manufacture. It is a further object to provide such an insert which incorporates a raised arch support region for better adaption to the foot of the user and which allows its use as a separate insert in existing footwear having the raised arch support. It is a further object to provide such a puncture proof insole insert which can be shaped for use as an orthotic device.